Grade of Bolts

Dear Readers,

Being a construction engineer, we very often use the bolts. Generally the grades of bolts are starts from 4.6 to 12.9. Also known as Ordinary bolt (Commercial Grade),  HT Bolt (High Tension) & HSFG Bolts (High Strength Friction Grip).

The bolt designation system is based on two numbers. The first number represents the ultimate tensile strength of the bolt, 400 MPa, 800 MPa or 1200 MPa respectively. The second number represents the point at which the bolt will permanently stretch. A 4.6 grade bolt permanently stretches at 60% of its ultimate, an 8.8 grade bolt at 80% and a 12.9 grade bolt at 90 % of its ultimate.

Technically it can be quoted that the first number is the tensile strength of the bolt material (N² )/100. The second number is = 1/100.(the ratio of the Proof (or Yield ) stress and the Tensile strength expressed as a percentage = 100.[Yield (Proof stress) /Tensile strength] /100

For Example the tensile and proof strength of the steel for a 8.8 bolt is therefore calculated as follows

Tensile strength = 8 X 100 N/mm² = 800 N/mm² and Proof strength = 0.8*800 * 100 /100 = 640 N/mm² (generally speaking 80% of 800N/mm2)

The lowest grade is 4.6, commonly known as commercial grade. Next comes grade 8.8, known as structural grade, and finally, the highest grade is 12.9, known as HT / HSFG bolt.

Available grade of bolts are 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9 & 12.9

For More Details about Torque Click Torque

For More Details about Torqe Calculation Click Calculation

For More Details about Slip Factor Click Factor

Best Quote. "Try not to become a man of success but a man of value". Have a Nice Day